It took a long time for nations to set a speed limit on the road to a warming world.
But for the past four years, even though negotiators have never arrived at a plan for avoiding dangerous climate change, they have agreed on a goal: limiting the increase in the Earth's global average surface temperature to 2°C (3.6°F) above the preindustrial level.
Now, two Union of Concerned Scientists (UCS) climate scientists and two colleagues argue that policymakers need to acknowledge that the world is already on track for warming beyond 2°C. (See related " Quiz: What You Don't Know About Climate Change Science .")
"A policy narrative that continues to frame this target as the sole metric of success or failure to constrain climate change risk is now itself becoming dangerous," wrote Todd Sanford and Peter Frumhoff of UCS in the commentary published Wednesday in Nature Climate Change. "(It) ill-prepares society to confront and manage the risks of a world that is increasingly likely to experience warming well in excess of 2°C this century," said the piece, co-authored by Amy Luers of the San Francisco-based Skoll Global Threats Fund, and Jay Gulledge, of the U.S. Department of Energy's Oak Ridge National Laboratory. (See a blog on the commentary by Gulledge.)
Rethinking the Target
The authors are by no means the first to suggest a rethinking of the 2°C goal. Todd Stern, the lead U.S. climate negotiator in President Barack Obama's administration, provoked anger in 2012 when he said a more "flexible, evolving" approach might be more effective in spurring a political accord. Coming at the issue from an entirely different angle, retired NASA climate scientist James Hansen and a group of colleagues wrote in December the 2°C target was not stringent enough, and " so dangerous" as to be "foolhardy ." At that level, the world risked initiating feedbacks in the climate system, such as the melting of ice sheet area, that could trigger irreversible warming out of humanity's control.
Hansen and colleagues suggested a 1°C target was far less dangerous. The Earth has warmed 0.85°C from 1880 (preindustrial times) to 2012, according to the latest consensus science reported in September by the Intergovernmental Panel on Climate Change (IPCC), the scientific body established by the United Nations to inform governments of climate risks.
The UCS scientists and colleagues took the IPCC to task for issuing reports that present different future scenarios, while making no judgment on the relative likelihood of the varying projections, "implicitly treating all scenarios as equivalently plausible." (...)
Wed Feb 26, 2014 2:35pm GMT
Clear evidence and uncertainty
Concentrations of carbon dioxide, the document notes, increased by 40 percent between 1880 and 2012 and are now higher than at any time in at least 800,000 years. As a result, global temperatures are 1.4 degrees Fahrenheit warmer than in 1900, Arctic sea ice is shrinking, sea levels are 8 inches higher, ocean acidity is on the rise, and the geographical ranges of many plants and animals are shifting.
"The evidence is clear," reads the report. "However, due to the nature of science, not every single detail is ever totally settled or completely certain. Nor has every pertinent question yet been answered."
Key areas of uncertainty highlighted in the report include the cause of the recent slowdown in warming, known as the hiatus; estimates of how much warming can be expected in the future; the connections between climate change and extreme weather events such as the frequency and intensity of hurricanes, droughts, and floods; and the role of clouds. (...)